Suddenly Website get down : Unable to found reason

Lightsail instances can slow down and appear as unresponsive when the instance consistently consumes more CPU than the Lightsail plan provides as a baseline. Lightsail uses burstable instance types that allow you to consume more CPU than your baseline for short periods of time. However, if an application continues to use more CPU beyond the plan's resources for long periods of time, the performance of the instance may suffer. This can happen for large or CPU intensive applications that run on a small plan size. To monitor your instance burst capacity, refer to: https://lightsail.aws.amazon.com/ls/docs/en_us/articles/amazon-lightsail-viewing-instance-burst-capacity